Insulin's interaction with its specific receptors in the plasma membrane of the adipose cell, is complex. The role of 125I-insulin and insulin receptor internalization in the mechanism of this interaction is under investigation. At 37 C, insulin binding to intact isolated rat adipose cells is associated with the rapid appearance of intact insulin in both endoplasmic reticulum- and Golgi-enriched membrane fractions. Concomitantly, insulin receptors are lost from the plasma membrane fraction and appear in the Golgi fraction. Steady state subellular distribution processes are insulin concentration dependent, and are inhibited at 16 C. The redistribution of the insulin receptor can be observed by measuring insulin binding to the receptor directly, by photoaffinity labeling the 138K receptor subunit, or by immunoprecipitating both the 138K and 95K receptor subunits following their iodination using lactoperoxidase. The receptor in the Golgi fraction, however, is accesible to insulin only in the presence of detergent. Thus, insulin induces a rapid, and insulin concentration- and temperature-dependent internalization of its own receptor from the plasma membrane to a Golgi-enriched membrane fraction through an endocytic-like process.